Study And Optimization On Storage Assignment Strategies In AS/RS

Automated Storage/Retrieval System (AS/RS)plays an important role in modern logistics, and multi-shuttle AS/RS is one of the major trends.The storage location assignment strategy is one of the key factors impacting on crane's travel time and system efficiency. Storage location assignment strategy and optimization in AS/RS system including multi-shuttle system are studied in this paper.Storage location assignment strategies for AS/RS systems with single shuttle, two shuttles and three shuttles are studied. A new kind of algorithm is developed for the optimization of storage location assignment, and 4 kinds of assignment strategies,random open location (ROL),closest open location (COL),longest waiting time retrieval (LWR) and nearest neighbor (NN),are analyzed.Quantitative analysis on the impact of different strategies on crane's travel time is conducted. Different strategies'sensitivities to the rack utilization are compared and their applicability is discussed.In the optimization process of storage location assignment, the optimization goal function is developed based on crane's weighted total travel time in single and dual command period. In sake of solving the problem, genetic algorithm is improved, first, the preferred selection operator is used to select the one has the highest fitness to the next generation;second, concept of the similarity is introduced in the crossover operation to select the chromos with lower similarity to crossover, it can keep the population diversity in order to avoid the premature convergence and increase the possibility of finding the optimal solution. Strategy of shortest weighted travel time in three kinds of AS/RS systems is solved with MATLAB,crane's travel time with different strategies is compared and analyzed, and in the three systems, rack utilization's impact on crane work efficiency with different strategies is studied.Finally, using discrete system simulation technology, simulation model that constructed with AutoMod imitate the work process and impact of rack utilization in AS/RS system, simulation results are compared and analyzed.